In order to prepare a composition for a patch preparation comprising a drug, a set of processes of dissolving a drug in a solvent such as an organic solvent, diluting the drug solution with a volatile solvent such as toluene and hexane which is easily evaporated, mixing the solution with an adhesive, extending the mixture product, and evaporating the volatile solvent to prepare a composition for a patch preparation (solvent method) have been typically used. In such case, the organic solvent used therein has been employed for serving as a transdermal absorption promoter as well as for dissolving a drug.
However, when a large volume of an organic solvent is used for dissolving a drug, the organic solvent can soften an adhesive layer in a tape preparation. As a result, the adhesibility of the tape preparation can be decreased, and also a part of an adhesive used in the adhesive layer can remain on the skin when the tape preparation is removed from the skin. In order to prevent such trouble caused by using a large volume of organic solvent, fillers are added to an adhesive to improve the lowered adhesibility (e.g. Patent Document 1).
Recently, some attempts to use a fatty acid-based ionic liquid as a solution for dissolving a drug or a transdermal absorption promoter have been made (e.g. Patent Document 2). However, a plaster base material used in a tape preparation is a SIS-based lipophilic plaster base material which has less affinity for a fatty acid based-ionic liquid because a fatty acid based-ionic liquid is in a salt form with high polarity, and thus such plaster base material has a tendency to be less miscible with the ionic liquid. As a result, a drug solution in which a drug is dissolved mainly in a fatty acid based-ionic liquid has a tendency to be easily separated from a lipophilic plaster base material.
Although a variety of means for solving these problems have been studied until now, drastic means have not been found.